The invention relates to a tempering system for hot water, more particularly, to a system that tempers the output of a hot water storage tank by mixing that output with a cold water flow in a defined ratio to produce a flow of water at a steady intermediate temperature.
It is desirable to maintain the temperature of water in a hot water storage tank as high as possible in order to kill bacteria and other growth organisms that multiply at tepid temperatures. However, unless tempered in some way, the scalding water discharged from such a tank may be dangerous to a consumer. Because of the potential danger the water temperature in many conventional water heater systems is maintained at or below approximately 140.degree. F.
Various systems have been proposed for maintaining a high water temperature in a hot water storage tank, and tempering the output. A number of systems use a heat exchanger arrangement in which the output of the storage tank is fed through a heat exchanger; the water gives up a portion of its heat to cold water entering the tank. One such system is disclosed in U.S. Pat. No. 5,115,491, which was granted to M. Perlman, J. M. Bell and C. A. McGugan on May 19, 1992. In that system a thermostat in the storage tank output and a bypass valve are used to adjust the flow of cold water through the heat exchanger based on the temperature of water leaving the tank; as that temperature drops, a larger part of the cold water flow is allowed to bypass the heat exchanger.
U.S. Pat. No. 3,007,470, granted to Heeger, and U.S. Pat. No. 3,958,555, granted to Horne, disclose other arrangements for maintaining water in a hot water storage tank at high temperature and tempering the output. Heeger utilizes two storage tanks, with water being transferred to a temperate water storage tank from a main hot water storage tank. The water in the two tanks is exchanged at a rate sufficient that temperate water is kept above a fixed minimum temperature. Horne discloses a system in which a hot water tank output flow is tempered, and then recirculated until use; the temperature of the recirculating water is maintained by a heat exchanger. The tempering systems of both Horne and Heeger are relatively complex.